Calibration Using Dual-Element Probes - GE USM 36 Series Technical Reference And Operating Manual

Calibrating the USM 36
You can read the material velocity and the probe delay
in the function group RANGE.
USM 36

Calibration using dual-element probes

Dual-element probes are especially used for wall thick-
ness measurements. The following special features
should be taken into account when using these probes:
V-path error
Dual-element probes produce a v-shaped sound path
from the pulser via the reflection from the backwall to the
receiver element. This V-path error affects the measur-
ing accuracy. You should therefore choose two wall
thicknesses that cover the expected thickness mea-
surement range for the calibration. In this way, the V-
path error can be corrected to a large extent.
Higher material velocity
Due to the V-path error, a higher material velocity than
that of the material to be tested is given during calibra-
tion, especially with small thicknesses. This is typical of
dual-element probes and serves for the compensation
of the V-path error.
Issue 2 (12/2013)
5 Operation
5-33